The present invention relates to an ignition control system for the ignition control in a cylinder of an internal-combustion engine, having an ignition coil whose primary winding is switched and having a secondary winding connected with a spark plug. The ignition control unit switches the primary winding by way of a first line and is connected with the secondary winding by way of a second line, the second line feeding an ionic current signal originating from the spark plug to the ignition control unit. A system of this type is known from German Patent document DE 101 38 976 A.
It is thus known to use the spark plug as a sensor for the ionic current, which is caused as a result of the combustion of an air-fuel mixture within the cylinder of the internal-combustion engine. The intensity of the ionic current significantly changes as a function of the combustion condition within the combustion chamber. By utilizing this effect, the combustion condition within the respective cylinder can be identified, and also the occurrence of a misfiring or knocking combustion in the internal-combustion engine can be determined.
If the primary winding and the secondary winding are components of a normal single-coil ignition system, that is, a system consisting of the respective spark plug and a pertaining ignition coil, which system is switched by the ignition control unit, at least four electric connecting contacts are obtained between the ignition control unit and the single-coil ignition system, specifically for the two potentials of the on-board power supply, the control of the primary winding, and the return of the ionic current signal.
In contrast, only three connecting contacts are required in the case of a conventional ignition control having a single-coil ignition system, that is, an ignition control without taking into account the ionic current signal. With respect to an internal-combustion engine having several cylinders, taking the ionic current signals into account leads to a basically different wiring construction. In addition, there are contact problems, which occur with each connecting contact and which rise proportionally with the number of connecting contacts.
It is an object of the invention to provide a system of the above-mentioned type, in which the number of the connecting contacts (and of the contact problems connected therewith) are kept to a minimum.
This object is achieved by the system for the ignition control in a cylinder of an internal-combustion engine, having an ignition coil whose primary winding is switched and having a secondary winding connected with a spark plug. The ignition control unit switches the primary winding by way of a first line and is connected with the secondary winding by way of a second line, the second line feeding an ionic current signal originating from the spark plug to the ignition control unit. A single line is used as the first and the second line. The operating direction of the line can be adjusted by different voltage levels applied to the line.
The invention utilizes a single electric line, which exists between the ignition control unit and the single-coil ignition system, as a current interface, which is operated in two directions. A current interface is always insensitive to ground offsets between the engine block and the ignition control unit. A ground offset is the difference of the reference potential (0V) between two spatially mutually separated electric circuits caused by electromagnetic radiation and/or current flow in connection with the impedance of the ground connection. A current interface normally has a current source (transmitter) and a current drain (receiver). By the establishment of two operating modes by way of the voltage levels, information can be transmitted in two directions successively with respect to time. As a result, only three connecting contacts are required between the ignition control unit and the single-coil ignition system.
The operating mode is differentiated by a voltage level which is clearly above or below 4 V. When the ignition control unit operates as a transmitter, that is, when it controls the primary winding of the ignition coil for the triggering of the ignition spark, it actively pulls the level of the line to the ground (OV) or leaves the line open passive, 4V or 0 mA). A switching circuit logic disposed in front of the ignition coil differs by way of the current occurring on the line with respect to an active or a passive line. A digital signal can thereby be transmitted to the switching circuit logic, by which the ignition is triggered.
Inversely, for transmitting the ionic current to the ignition control unit, the voltage level of the line is adjusted to 8V. Then, in the ignition coil, the switching circuit logic impresses the ionic current on the line. The engine timing gear can determine and process this current by way of a precision resistor. This differentiation of the two line signals between analog and digital additionally facilitates the recognition of the operating direction of the current interface.
If the ionic current is additionally detected in the switching logic, the resistance to interferences will clearly be improved because the ionic current situated in the uA range is already treated close to the spark plug.
For this purpose, it may be advantageous to additionally provide an amplifier circuit in the switching logic for the ionic current signal originating from the secondary winding. As a result, the lowest ionic currents can also be detected.
A further improvement is obtained when the amplifier circuit is controlled in its amplification factor corresponding to the intensity of the ionic current. This control can advantageously be carried out from the ignition control unit. The amplification is the greater, the weaker the ionic current signal is at first.
For this purpose, the amplification factor is defined as a digital signal by the ignition control unit. This signal is therefore digital like the ignition signal and differs from the latter essentially with respect to the point in time at which it is emitted.
If this digital signal is emitted by the ignition control unit at the start within a power cycle for a cylinder, a danger of a collision with the ignition control signal is averted.
The amplification factor itself may be determined by the intensity of the ionic current signal in the preceding power cycle of the cylinder. Since the already amplified ionic current signal arrives at the ignition control unit and the ignition control unit knows the amplification factor used as the basis, it can, in each case, adapt the factor when the amplified ionic current signal changes. In this manner, the ionic current signal arriving in the ignition control unit can be kept in an optimal modulation range with respect to the signal-to-noise ratio without encountering the modulation limits.
Furthermore, the amount of the measuring voltage, as described above for the amplification factor, can also be defined as the digital signal by the ignition control unit.
As a result, when the ionic current signal is sufficiently high, the measuring voltage can be reduced in order to keep the power loss to a minimum when generating the measuring voltage. In addition, with a lower measuring voltage, less energy is also withdrawn from the ignition spark. Since the measuring voltage is added to the secondary high switch-on voltage occurring when the primary winding is switched on, the resulting voltage over the spark plug is unnecessarily increased, whereby the danger of undesired pre-ignitions is reduced.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.